Subunit Of L-type Calcium Channel Research Articles

Abstract 11273: Caveolae-Specific Phosphorylation of L-type Calcium Channel β2a Subunit Exacerbates Cardiac Hypertrophy

Background: L-type calcium channel (LTCC) localizes at T-tubules and caveolae in cardiomyocytes, and plays major roles in excitation-contraction coupling and cardiac hypertrophy. The expression of β2a subunit of LTCC (β2a) is increased in human failing heart. Recently, it was reported that phosphorylation of β2a by CaMKII enhanced LTCC activity. However, the functional role of β2a phosphorylation in heart failure remains to be elucidated. Objective: To make clear the functional role of β2a phosphorylation in cardiomyocytes. Methods and Results: Adenoviral overexpression of β2a demonstrated its constitutive phosphorylation by CaMKII and induced neonatal cardiomyocyte hypertrophy. Interestingly, phosphorylated β2a was co-localized with caveolin3. To assess caveolae-specific activation of CaMKII, we generated a fusion protein composed of phospholamban and caveolin3 (PLN-Cav3). This protein localized at caveolae, and caveolae-specific activation of CaMKII was detected using phospho-specific antibody for PLN (Thr17). In addition, to inhibit caveolae-specific CaMKII activity, we developed a GFP fusion protein with caveolin binding domain fused to CaMKII inhibitory peptide (CBD-GFP-AIP). We identified that this protein co-localized with caveolin3, and inhibited activation of CaMKII specifically at caveolae using PLN-Cav3 method. Moreover, CBD-GFP-AIP abolished β2a phosphorylation and attenuated β2a-induced cardiac hypertrophy. We found that phenylephrine (PE) stimulation activated caveolae-CaMKII and β2a in vitro and in vivo. Finally, we generated transgenic mice overexpressing wild-type (w-TG) or non-phospho mutant β2a (m-TG) in cardiomyocyte and evaluated cardiac hypertrophy after two weeks of chronic PE stimulation. The expression of β2a in both TG increased approximately 2.5 fold compared to control mice. PE-induced cardiac hypertrophy was attenuated in m-DTG compared to w-DTG mice (heart weight-body weight ratio: control; 4.8±0.2, *w-TG; 5.5±0.3, m-TG; 4.8±0.4, n=5-6, *p<0.05 vs others). Conclusion: We developed novel methods to evaluate and inhibit caveolae-specific activation of CaMKII. Using these methods, we revealed that phosphorylated β2a localized at caveolae, and exaggerates cardiac hypertrophy.

Functional implications of a psychiatric risk variant within CACNA1C in induced human neurons.

Psychiatric disorders have clear heritable risk. Several large-scale genome-wide association studies have revealed a strong association between susceptibility for psychiatric disorders, including bipolar disease, schizophrenia, and major depression, and a haplotype located in an intronic region of the L-type voltage gated calcium channel (VGCC) subunit gene CACNA1C (peak associated SNP rs1006737), making it one of the most replicable and consistent associations in psychiatric genetics. In the current study, we used induced human neurons to reveal a functional phenotype associated with this psychiatric risk variant. We generated induced human neurons, or iN cells, from more than 20 individuals harboring homozygous risk genotypes, heterozygous, or homozygous non-risk genotypes at the rs1006737 locus. Using these iNs, we performed electrophysiology and quantitative PCR experiments that demonstrated increased L-type VGCC current density as well as increased mRNA expression of CACNA1C in induced neurons homozygous for the risk genotype, compared to non-risk genotypes. These studies demonstrate that the risk genotype at rs1006737 is associated with significant functional alterations in human induced neurons, and may direct future efforts at developing novel therapeutics for the treatment of psychiatric disease.

Rare mutations of CACNB2 found in autism spectrum disease-affected families alter calcium channel function.

Autism Spectrum Disorders (ASD) are complex neurodevelopmental diseases clinically defined by dysfunction of social interaction. Dysregulation of cellular calcium homeostasis might be involved in ASD pathogenesis, and genes coding for the L-type calcium channel subunits CaV1.2 (CACNA1C) and CaVβ2 (CACNB2) were recently identified as risk loci for psychiatric diseases. Here, we present three rare missense mutations of CACNB2 (G167S, S197F, and F240L) found in ASD-affected families, two of them described here for the first time (G167S and F240L). All these mutations affect highly conserved regions while being absent in a sample of ethnically matched controls. We suggest the mutations to be of physiological relevance since they modulate whole-cell Ba2+ currents through calcium channels when expressed in a recombinant system (HEK-293 cells). Two mutations displayed significantly decelerated time-dependent inactivation as well as increased sensitivity of voltage-dependent inactivation. In contrast, the third mutation (F240L) showed significantly accelerated time-dependent inactivation. By altering the kinetic parameters, the mutations are reminiscent of the CACNA1C mutation causing Timothy Syndrome, a Mendelian disease presenting with ASD. In conclusion, the results of our first-time biophysical characterization of these three rare CACNB2 missense mutations identified in ASD patients support the hypothesis that calcium channel dysfunction may contribute to autism.

A Timothy Syndrome Causing Mutation Perturbs Voltage Sensor Operation in Human CaV1.2 Channels

The pore-forming α1C subunit of the voltage-gated L-type calcium channel (CaV1.2) consists of four concatenated Repeats (I-IV), each contributing a voltage-sensing domain (VSD, transmembrane helices S1-S4) and a quarter of the central ion-conductive pore domain (S5-S6). In Timothy Syndrome (TS), a rare and severe multi-organ disorder, specific alterations in CaV1.2 voltage-dependent properties lead to autism, immunodeficiency, QT prolongation (LQT8) and lethal arrhythmias. The most frequent TS-causing mutation (G406R) is located at the intracellular flank of S6 in Repeat I and promotes Ca2+ influx by (1) shifting CaV1.2 voltage- dependent activation towards more negative potentials and (2) impairing voltage-dependent inactivation. To gain insight on the molecular basis underlying the TS-causing voltage-sensitivity anomalies, we studied the structural rearrangements of VSDs I and III in human CaV1.2 channels carrying the G406R mutation, using the voltage-clamp fluorometry technique. Briefly, this involves conjugating a small, environment-sensitive fluorophore at a specific VSD that reports local conformational rearrangements as fluorescence changes. Under voltage-clamp, we simultaneously acquired ionic current and fluorescence signals, which corresponded to specific VSD rearrangements during channel activation. We found that the G406R mutation dramatically altered the operation of VSDs I and III compared to wild-type channels, by inducing a hyperpolarizing shift in their activation voltage dependence of ∼80mV and ∼50mV, respectively. These shifts were associated with a significant reduction in the effective valences of VSD I and III by ∼50% and ∼42%, respectively. Moreover, the sign of the fluorescence signals detected from TS channels was opposite to that observed in wild-type CaV1.2 channels. Taken together, these results suggest that the TS-causing mutation causes an overall structural perturbation, manifested as a change in both the fluorophore quenching process reported from VSD I and VSD III and their altered voltage-dependence. Funded by: NIH,AHA,FONDECYT,ACT.

Quantitative proteome analysis of age‐related changes in mouse gastrocnemius muscle using mTRAQ

Aging is associated with a progressive loss of skeletal muscular function that often leads to progressive disability and loss of independence. Although muscle aging is well documented, the molecular mechanisms of this condition still remain unclear. To gain greater insight into the changes associated with aging of skeletal muscle, we performed quantitative proteomic analyses on young (6 months) and aged (27 months) mouse gastrocnemius muscles using mTRAQ stable isotope mass tags. We identified and quantified a total of 4585 peptides corresponding to 236 proteins (protein probability >0.9). Among them, 33 proteins were more than 1.5-fold upregulated and 20 proteins were more than 1.5-fold downregulated in aged muscle compared with young muscle. An ontological analysis revealed that differentially expressed proteins belonged to distinct functional groups, including ion homeostasis, energy metabolism, protein turnover, and Ca(2+) signaling. Identified proteins included aralar1, β-enolase, fatty acid-binding protein 3, 3-hydroxyacyl-CoA dehydrogenase (Hadh), F-box protein 22, F-box, and leucine-rich repeat protein 18, voltage-dependent L-type calcium channel subunit beta-1, ryanodine receptor (RyR), and calsequestrin. Ectopic expression of calsequestrin in C2C12 myoblast resulted in decreased activity of nuclear factor of activated T-cells and increased levels of atrogin-1 and MuRF1 E3 ligase, suggesting that these differentially expressed proteins are involved in muscle aging.

Attenuated response of L-type calcium current to nitric oxide in atrial fibrillation

Nitric oxide (NO) synthesized by cardiomyocytes plays an important role in the regulation of cardiac function. Here, we studied the impact of NO signalling on calcium influx in human right atrial myocytes and its relation to atrial fibrillation (AF). Right atrial appendages (RAAs) were obtained from patients in sinus rhythm (SR) and AF. The biotin-switch technique was used to evaluate endogenous S-nitrosylation of the α1C subunit of L-type calcium channels. Comparing SR to AF, S-nitrosylation of Ca(2+) channels was similar. Direct effects of the NO donor S-nitroso-N-acetyl-penicillamine (SNAP) on L-type calcium current (ICa,L) were studied in cardiomyocytes with standard voltage-clamp techniques. In SR, ICa,L increased with SNAP (100 µM) by 48%, n/N = 117/56, P < 0.001. The SNAP effect on ICa,L involved activation of soluble guanylate cyclase and protein kinase A. Specific inhibition of phosphodiesterase (PDE)3 with cilostamide (1 µM) enhanced ICa,L to a similar extent as SNAP. However, when cAMP was elevated by PDE3 inhibition or β-adrenoceptor stimulation, SNAP reduced ICa,L, pointing to cGMP-cAMP cross-regulation. In AF, the stimulatory effect of SNAP on ICa,L was attenuated, while its inhibitory effect on isoprenaline- or cilostamide-stimulated current was preserved. cGMP elevation with SNAP was comparable between the SR and AF group. Moreover, the expression of PDE3 and soluble guanylate cyclase was not reduced in AF. NO exerts dual effects on ICa,L in SR with an increase of basal and inhibition of cAMP-stimulated current, and in AF NO inhibits only stimulated ICa,L. We conclude that in AF, cGMP regulation of PDE2 is preserved, but regulation of PDE3 is lost.

Manipulating L-type calcium channels in cardiomyocytes using split-intein protein transsplicing

Manipulating expression of large genes (>6 kb) in adult cardiomyocytes is challenging because these cells are only efficiently transduced by viral vectors with a 4-7 kb packaging capacity. This limitation impedes understanding structure-function mechanisms of important proteins in heart. L-type calcium channels (LTCCs) regulate diverse facets of cardiac physiology including excitation-contraction coupling, excitability, and gene expression. Many important questions about how LTCCs mediate such multidimensional signaling are best resolved by manipulating expression of the 6.6 kb pore-forming α1C-subunit in adult cardiomyocytes. Here, we use split-intein-mediated protein transsplicing to reconstitute LTCC α1C-subunit from two distinct halves, overcoming the difficulty of expressing full-length α1C in cardiomyocytes. Split-intein-tagged α1C fragments encoding dihydropyridine-resistant channels were incorporated into adenovirus and reconstituted in cardiomyocytes. Similar to endogenous LTCCs, recombinant channels targeted to dyads, triggered Ca(2+) transients, associated with caveolin-3, and supported β-adrenergic regulation of excitation-contraction coupling. This approach lowers a longstanding technical hurdle to manipulating large proteins in cardiomyocytes.

Effect of lead sulfide nanoparticles exposure on calcium homeostasis in rat hippocampus neurons

PbS nanoparticles (NPs) is an important nanomaterial for biomedical imaging in living tissues. However, concerning the high toxicity, especially neurotoxicity, of Pb element, it is crucial that the toxicity assessment of “naked” PbS NPs should be adequately studied. In the current study, we systematically explored the neurotoxicity of PbS NPs in rats by measuring the body weight and brain coefficient changes, testing memory behaviors in Y-electric maze, and studying the neuronal ultrastructure and pathology in hippocampus. Furthermore, in order to study the toxic mechanism, we performed Pb and Ca content measurements in various organs, and investigated Ca2+-ATPase activity and L-type calcium channel subunit expression. Our results confirmed that PbS NPs showed high neurotoxicity, while a possible mechanism was suggested to be due to the PbS NPs-induced calcium homeostasis disorder which was caused by the abnormal calcium transportation.

Identification of risk loci with shared effects on five major psychiatric disorders: a genome-wide analysis

Findings from family and twin studies suggest that genetic contributions to psychiatric disorders do not in all cases map to present diagnostic categories. We aimed to identify specific variants underlying genetic effects shared between the five disorders in the Psychiatric Genomics Consortium: autism spectrum disorder, attention deficit-hyperactivity disorder, bipolar disorder, major depressive disorder, and schizophrenia.We analysed genome-wide single-nucleotide polymorphism (SNP) data for the five disorders in 33,332 cases and 27,888 controls of European ancestory. To characterise allelic effects on each disorder, we applied a multinomial logistic regression procedure with model selection to identify the best-fitting model of relations between genotype and phenotype. We examined cross-disorder effects of genome-wide significant loci previously identified for bipolar disorder and schizophrenia, and used polygenic risk-score analysis to examine such effects from a broader set of common variants. We undertook pathway analyses to establish the biological associations underlying genetic overlap for the five disorders. We used enrichment analysis of expression quantitative trait loci (eQTL) data to assess whether SNPs with cross-disorder association were enriched for regulatory SNPs in post-mortem brain-tissue samples.SNPs at four loci surpassed the cutoff for genome-wide significance (p<5×10(-8)) in the primary analysis: regions on chromosomes 3p21 and 10q24, and SNPs within two L-type voltage-gated calcium channel subunits, CACNA1C and CACNB2. Model selection analysis supported effects of these loci for several disorders. Loci previously associated with bipolar disorder or schizophrenia had variable diagnostic specificity. Polygenic risk scores showed cross-disorder associations, notably between adult-onset disorders. Pathway analysis supported a role for calcium channel signalling genes for all five disorders. Finally, SNPs with evidence of cross-disorder association were enriched for brain eQTL markers.Our findings show that specific SNPs are associated with a range of psychiatric disorders of childhood onset or adult onset. In particular, variation in calcium-channel activity genes seems to have pleiotropic effects on psychopathology. These results provide evidence relevant to the goal of moving beyond descriptive syndromes in psychiatry, and towards a nosology informed by disease cause.National Institute of Mental Health.

Identification of In Vivo, Conserved, TAF15 RNA Binding Sites Reveals the Impact of TAF15 on the Neuronal Transcriptome

RNA binding proteins (RBPs) have emerged as major causative agents of amyotrophic lateral sclerosis (ALS). To investigate the function of TAF15, an RBP recently implicated in ALS, we explored its target RNA repertoire in normal human brain and mouse neurons. Coupling high-throughput sequencing of immunoprecipitated and crosslinked RNA with RNA sequencing and TAF15 knockdowns, we identified conserved TAF15 RNA targets and assessed the impact of TAF15 on the neuronal transcriptome. We describe a role of TAF15 in the regulation of splicing for a set of neuronal RNAs encoding proteins with essential roles in synaptic activities. We find that TAF15 is required for a critical alternative splicing event of the zeta-1 subunit of the glutamate N-methyl-D-aspartate receptor (Grin1) that controls the activity and trafficking of NR1. Our study uncovers neuronal RNA networks impacted by TAF15 and sets the stage for investigating the role of TAF15 in ALS pathogenesis.

Sequence capture and massively parallel sequencing to detect mutations associated with malignant hyperthermia

Malignant hyperthermia (MH) is a potentially fatal pharmacogenetic disorder in which intracellular calcium homeostasis in the skeletal muscle of susceptible individuals is disrupted upon exposure to halogenated anaesthetics. While MH is linked to the ryanodine receptor (RYR1) on chromosome 19 and the α1S subunit of the voltage-dependent L-type calcium channel (CACNA1S) on chromosome 1, mutations have been found in only 50-70% of patients, and subsequently, there is a need for a more powerful screening tool. Genomic DNA capture and next-generation sequencing was used to screen 32 genes involved in excitation-contraction coupling, skeletal muscle calcium homeostasis, or immune response in two MH patients. Lymphoblastoid cell lines were used to functionally characterize candidate RYR1 mutations in one family. Sequence analysis revealed two putative causative mutations in RYR1 in one patient. Segregation analysis and functional analysis support a causative role of the detected variants. The amount of Ca(2+) released after stimulation with 4-chloro-m-cresol from B lymphocytes of the MH-susceptible patients in the family was significantly greater compared with that of Ca(2+) released from cells of an MH-negative family member. In the other patient, no causative mutations were identified in the 32 genes screened. In this study, we successfully demonstrate the use of genomic DNA capture and next-generation sequencing for identification of putative mutations causing MH. We also suggest that whole exome sequencing may be necessary to identify MH causing mutations in patients where no mutations in RYR1 and CACNA1S have been identified thus far.

Inhibition of glucocorticoid receptors ameliorates hypobaric hypoxia induced memory impairment in rat

Chronic exposure to hypobaric hypoxia (HH) causes neurodegeneration and loss of memory. The underlying mechanisms of HH induced memory impairment have been attributed to prolonged elevated corticosterone level in hippocampus leading to augmented glutamate excitotoxicity, oxidative stress, alteration of neurotransmitter level or their receptors and calcium mediated signaling. Whether this corticosterone mediated neurodegenerative effect occurs through overstimulation of glucocorticoid receptors (GRs) or is independent of the GRs, is not known. Four groups of rats were taken and GR blocker mifepristone was administered intraperitoneally during exposure to HH from 3rd to 7th days. Our results showed a duration dependent transcriptional upregulation of GRs and MRs following exposure to HH. Prolonged exposure to HH for 7 days augmented the translocation of GRs from cytosol to nucleus. Inhibition of GRs during hypoxic exposure improved the hippocampal ATP level and modulated the apoptotic markers like p53, Bcl2 and Bax. Decreased expression of L-type calcium channel and NR1 subunit of NMDA receptors were also observed following administration of mifepristone during hypoxic exposure. Morphological studies following mifepristone administration during hypoxic exposure showed decreased number of pyknotic cells in hippocampus and decrease in apoptotic and necrotic cells in the CA3 region of hippocampus. The study indicates that elevated corticosterone level during hypoxic exposure causes neurodegeneration and acts through its binding to GRs indicating that inhibition of GRs may provide therapeutic effect in ameliorating HH induced memory impairment.

Evidence for a vast peptide overlap between West Nile virus and human proteomes

The primary amino acid sequence of West Nile virus (WNV) polyprotein, GenBank accession number M12294, was analyzed by computional biology. WNV is a mosquito-borne neurotropic flavivirus that has emerged globally as a significant cause of viral encephalitis in humans. Using pentapeptides as scanning units and the perfect peptide match program from PIR International Protein Sequence Database, we compared the WNV polyprotein and the human proteome. WNV polyprotein showed significant sequence similarities to a number of human proteins. Several of these proteins are involved in embryogenesis, neurite outgrowth, cortical neuron branching, formation of mature synapses, semaphorin interactions, and voltage dependent L-type calcium channel subunits. The biocomputional study suggest that common amino acid segments might represent a potential platform for further studies on the neurological pathophysiology of WNV infections.

Calcium regulates caveolin-1 expression at the transcriptional level

Caveolin-1, an indispensable component of caveolae serving as a transformation suppressor protein, is highly expressed in poorly metastatic mouse osteosarcoma FBJ-S1 cells while highly metastatic FBJ-LL cells express low levels of caveolin-1. Calcium concentration is higher in FBJ-S1 cells than in FBJ-LL cells; therefore, we investigated the possibility that calcium signaling positively regulates caveolin-1 in mouse FBJ-S1 cells. When cells were treated with the calcium channel blocker nifedipine, cyclosporin A (a calcineurin inhibitor), or INCA-6 (a nuclear factor of activated T-cells [NFAT] inhibitor), caveolin-1 expression at the mRNA and protein levels decreased. RNA silencing of voltage-dependent L-type calcium channel subunit alpha-1C resulted in suppression of caveolin-1 expression. This novel caveolin-1 regulation pathway was also identified in mouse NIH 3T3 cells and Lewis lung carcinoma cells. These results indicate that caveolin-1 is positively regulated at the transcriptional level through a novel calcium signaling pathway mediated by L-type calcium channel/Ca2+/calcineurin/NFAT.

High-Resolution Optical Imaging of Zebrafish Larval Ribbon Synapse Protein RIBEYE, RIM2, and CaV 1.4 by Stimulation Emission Depletion Microscopy

The synaptic ribbon is a unique presynaptic structure with an intricate morphology in photoreceptors. Because of the resolution limit in conventional fluorescence microscopy, investigating ribbon protein locations has been challenging, especially in the early development stages of model animals. Here, we used stimulated emission depletion microscopy, a super-resolution imaging technique, to look at retina sections in 4 days post-fertilization (dpf) zebrafish. We observed that in photoreceptor cells, RIBEYE and RIM2 are expressed along the synaptic ribbon, with RIM2 consistently located inside of the horseshoe-shaped synaptic ribbon structure with RIBEYE located on the outside. The L-type calcium channel subunit, CACNA1F, exhibited small spot-like staining beneath the RIM2 and RIBEYE structures. Using morpholino antisense oligonucleotides to knock down RIBEYE expression, we observed fewer and shorter ribbons in the photoreceptor outer plexiform layers of 4 dpf fish retina as well as a reduction in RIM2 expression. The clustering of CACNA1F in these blind fish was no longer observed, but instead showed a diffuse expression in the photoreceptor terminal.

Upregulation of CaMKIIδ during ischaemia–reperfusion is associated with reperfusion-induced arrhythmias and mechanical dysfunction of the rat heart: involvement of sarcolemmal Ca2+-cycling proteins

Although Ca(2+)/calmodulin-dependent protein kinase II delta (CaMKIIδ) has been implicated in development of different phenotypes of myocardial ischaemia-reperfusion injury, its involvement in arrhythmogenesis and cardiac stunning is not sufficiently elucidated. Moreover, the mechanisms by which CaMKIIδ mediates disturbances in excitation-contraction coupling, are not exactly known. To investigate this, KN-93 (0.5 µmol/L), a CaMKII inhibitor, was administered before induction of global ischaemia and reperfusion in isolated Langendorff-perfused rat hearts. Expression of CaMKIIδ and the sarcollemal Ca(2+)-cycling proteins, known to be activated during reperfusion, was analyzed using immunoblotting. KN-93 reduced reperfusion-induced ectopic activity and the incidence of ventricular fibrillation. Likewise, the severity of arrhythmias was lower in KN-treated hearts. During the pre-ischaemia phase, neither inotropic nor chronotropic effects were elicited by KN-93, whereas post-ischaemic contractile recovery was significantly improved. Ischaemia-reperfusion increased the expression of CaMKIIδ and sodium-calcium exchanger (NCX1) proteins without any influence on the protein content of alpha 1c, a pore-forming subunit of L-type calcium channels (LTCCs). On the other hand, inhibition of CaMKII normalized changes in the expression of CaMKIIδ and NCX1. Taken together, CaMKIIδ seems to regulate its own turnover and to be an important component of cascade integrating NCX1, rather than LTCCs that promote ischaemia-reperfusion-induced contractile dysfunction and arrhythmias.

KSHV induces rapid release of angiopoietin-2 from endothelial cells to promote angiogenesis and inflammation

The development of Kaposi’s sarcoma (KS), the most common malignancy in AIDS patients, results from Kaposi’s sarcoma-associated herpesvirus (KSHV) infection of endothelial cells and subsequent induction of proliferation, angiogenesis, and inflammation. Previously, we demonstrated that KSHV infection of human umbilical vein endothelial cells (HUVEC) induced a transcriptional induction of Angiopoietin-2 (Ang-2), a pro-angiogenic and pro-inflammatory cytokine that is highly present in KS tumors. This transcriptional up-regulation of Ang-2 started at 12 h and peaked at 54 h post-infection. In difference to our previous data, here we demonstrate that KSHV infection of HUVEC induces rapid release of Ang-2 within minutes of viral contact. Pre-made Ang-2 is stored in the Weibel-Palade body in endothelial cells and is released through regulated exocytosis. KSHV binding to HUVEC is responsible for rapid Ang-2 release because blockade of viral binding inhibits this cytokine exocytosis. We find that KSHV binding to its integrin receptors on endothelial cells activates the integrin tyrosine kinase receptors signaling pathways, including tyrosine phosphorylation of the kinases FAK and Src, and triggers rapid calcium mobilization. This mobilization likely plays a key role in mediating Ang-2 release, as its inhibition by various calcium chelators and calcium channel blockers substantially reduces Ang-2 release. We also demonstrate a direct interaction and association of the kinase Src with the alpha1C subunit of L-type calcium channel. Indeed, specific inhibitors of protein tyrosine phosphorylation not only disrupt this interaction but also abolish Ang-2 release. Finally, preliminary data from in vitro cell adhesion assays suggest that this rapidly released Ang-2 enhances migration and adhesion of monocytes to the infected endothelial cells. To our knowledge, this is the first demonstration of interaction between KSHV and its integrins receptors in regulating rapid cytokine release. This study also uncovers a novel mechanism of KSHV induction of angiogenesis and inflammation, which is much faster, and could likely play important roles in the early event of KS tumor development.

227 CALCIUM CHANNEL BLOCKER MODULATES ANDROGEN RECEPTOR-MEDIATED GENE EXPRESSION AND INDUCES CYTOTOXICITY IN PROSTATE CANCER CELLS

INTRODUCTION AND OBJECTIVES: Calcium (Ca ), a ubiquitous secondary messenger, is involved in several cellular processes such as apoptosis, proliferation and carcinogenesis. It has also been shown that Ca signaling is involved in androgen-induced PSA secretion. Recently published epidemiologic data demonstrated that patients on calcium channel blockers had significantly lower incidences of prostate cancer. Therefore, we examined the role of various voltagegated calcium channels in androgen signaling and prostate cancer development. METHODS: Multiple prostate cancer cell lines including LNCaP, LAPC-4, and C4-2 (all androgen receptor positive) were treated with calcium channel blockers nifedipine, mibefradil, and tetrandine. The medications were added to the cell culture media at a dose range of 5-50 micromolar for various time points between 2 and 24 hours. Cell proliferaion was measured using an MTS assay. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to determine expression of several Ca channel genes in different cell lines. Knockdown of Ca channel expression using an siRNA was also utilized to determine effects on cell lines. RESULTS: Blocking L-type channels with nifedipine and tetrandrine significantly suppressed cell proliferation and androgen receptormediated gene expression in prostate cancer cells. Higher doses of tetrandrine also induced a dramatic cytotoxic effect. In contrast, a T-type specific channel blocker mibefradil induced androgen receptor transactivation without androgen addition and also drastically enhanced androgen receptor transactivation in a reporter gene assay. RT-PCR demonstrated that only L-type CACNA1D (cav1.3) and T-type CACNA1H (cav3.2) alpha-subunit genes are highly expressed in androgen receptor-positive prostate cancer cell lines, while L-type CACNA1F (cav1.4) is only weakly expressed in androgen receptorpositive cell lines but highly expressed in androgen receptor-negative cell lines. Other subunits are not expressed in any prostate cancer cells. Furthermore, consistently, knocking down CACNA1D (cav1.3) expression by the siRNA approach abrogated AR transactivation while knocking down CACNA1H (cav3.2) expression enhanced AR transactivation. CONCLUSIONS: These results suggest that the L-type calcium channel subunit (cav1.3) has the potential as a therapeutic target for prostate cancer intervention, although further clinical testing is warranted.

Defective calcium inactivation causes long QT in obese insulin-resistant rat

The majority of diabetic patients who are overweight or obese die of heart disease. We suspect that the obesity-induced insulin resistance may lead to abnormal cardiac electrophysiology. We tested this hypothesis by studying an obese insulin-resistant rat model, the obese Zucker rat (OZR). Compared with the age-matched control, lean Zucker rat (LZR), OZR of 16-17 wk old exhibited an increase in QTc interval, action potential duration, and cell capacitance. Furthermore, the L-type calcium current (I(CaL)) in OZR exhibited defective inactivation and lost the complete inactivation back to the closed state, leading to increased Ca(2+) influx. The current density of I(CaL) was reduced in OZR, whereas the threshold activation and the current-voltage relationship of I(CaL) were not significantly altered. L-type Ba(2+) current (I(BaL)) in OZR also exhibited defective inactivation, and steady-state inactivation was not significantly altered. However, the current-voltage relationship and activation threshold of I(BaL) in OZR exhibited a depolarized shift compared with LZR. The total and membrane protein expression levels of Cav1.2 [pore-forming subunit of L-type calcium channels (LTCC)], but not the insulin receptors, were decreased in OZR. The insulin receptor was found to be associated with the Cav1.2, which was weakened in OZR. The total protein expression of calmodulin was reduced, but that of Cavβ2 subunit was not altered in OZR. Together, these results suggested that the 16- to 17-wk-old OZR has 1) developed cardiac hypertrophy, 2) exhibited altered electrophysiology manifested by the prolonged QTc interval, 3) increased duration of action potential in isolated ventricular myocytes, 4) defective inactivation of I(CaL) and I(BaL), 5) weakened the association of LTCC with the insulin receptor, and 6) decreased protein expression of Cav1.2 and calmodulin. These results also provided mechanistic insights into a remodeled cardiac electrophysiology under the condition of insulin resistance, enhancing our understanding of long QT associated with obese type 2 diabetic patients.

PI3Kγ inhibition reduces blood pressure by a vasorelaxant Akt/L-type calcium channel mechanism

The lipid and protein kinase phosphoinositide 3-kinase γ (PI3Kγ) is abundantly expressed in inflammatory cells and in the cardiovascular tissue. In recent years, its role in inflammation and in cardiac function and remodelling has been unravelled, highlighting the beneficial effects of its pharmacological inhibition. Furthermore, a role for PI3Kγ in the regulation of vascular tone has been emphasized. However, the impact of this signalling in the control of blood pressure is still poorly understood. Our study investigated the effect of a selective inhibition of PI3Kγ, obtained by using two independent small molecules, on blood pressure. Moreover, we dissected the molecular mechanisms involved in control of contraction of resistance arteries by PI3Kγ. We showed that inhibition of PI3Kγ reduced blood pressure in normotensive and hypertensive mice in a concentration-dependent fashion. This effect was dependent on enhanced vasodilatation, documented in vivo by decreased peripheral vascular resistance, and ex vivo by vasorelaxing effects on isolated resistance vessels. The vasorelaxation induced by PI3Kγ inhibition relied on blunted pressure-induced Akt phosphorylation and a myogenic contractile response. Molecular insights revealed that PI3Kγ inhibition affected smooth muscle L-type calcium channel current density and calcium influx by impairing plasma membrane translocation of the α1C L-type calcium channel subunit responsible for channel open-state probability. Overall our findings suggest that PI3Kγ inhibition could be a novel tool to modulate calcium influx in vascular smooth muscle cells, thus relaxing resistance arteries and lowering blood pressure.